Exo-tetrahydrodicyclopentadiene (exo-THDCPD) is a high density liquid missile fuel. This single component fuel, also known as JP-10 is obtained by hydrogenation of dicyclopentadiene (DCPD) to endo tetrahydro-dicyclopentadiene (endo-THDCPD) and the isomerization of endo-THDCPD to the exo-THDCPD isomer. The exo-THDCPD isomer has a melting point of −79° C. and is the main component of JP-10. The endo-THDCPD has a freezing point of +77° C. and is therefore not a good candidate for high density liquid fuel.
In the manufacture of exo-THDCPD, the hydrogenation of the DCPD is fairly straight forward. The feed of DCPD, which is mostly the endo-isomer, is kept in solution by dissolution into a paraffinic solvent (i.e., mostly linear paraffin of C6-C9). The hydrotreated stream, which is mostly an endo-isomer, is then isomerized to the exo-isomer. The finished product exo-THDCPD of greater than 98% purity is then produced by distillation of the isomerized stream.
In the manufacture of exo-THDCPD, isomerization of the endo-THDCPD to exo-THDCPD is the most difficult processing step. Various acidic catalysts have been used to facilitate the isomerization reaction.
In the prior art. JP-10 is prepared by first completely hydrogenating extra-high purity cyclopentadiene (CPD) dimer, namely dicyclopentadiene (DCPD, freezing point of 33.6° C.), as a precursor to yield the solid endo-isomer of the hydrogenated derivative, namely endo-THDCPD (freezing point of 77° C.), wherein the hydrogenation of DCPD is carried out in two stages. In the first stage, the dihydro derivative, namely dihydrodicyclopentadiene (DHDCPD, freezing point of 51° C.) was obtained by selective hydrogenation of DCPD in the presence of nickel or palladium catalyst at a temperature of 50-120° C. In the second stage, the solid endo-THDCPD (freezing point of 77° C.) was obtained by hydrogenation of DHDCPD in the presence of metal catalyst at a temperature of 130-220° C. Finally, the solid endo-THDCPD is isomerized to the liquid exo-THDCPD, namely JP-10 (freezing point <−79° C.), in an amount of more than 98.5% of the total product weight in the presence of an acidic catalyst. JP-10 is very expensive because it is obtained by chemical synthesis from extra-high purity DCPD using a batch reactor (referring to U.S. Pat. Nos. 3,381,046; 4,086,284; 4,107,223 and 4,270,014).
Isomerization of endo-hydrogenated dicyclopentadiene compounds to form the exo-isomer have generally involved the use of solid acid catalysts that are either supported in a fixed bed type reactor or suspended in a slurry type reactor. Because suspended solid catalysts are difficult to handle, it is desirable to employ a liquid catalyst.